Plastic-Eating Bacteria Engineered to Convert Waste Into Biodegradable Spider Silk [Study]

Scientists found a way to transform plastic waste into biodegradable spider silk using bacteria. The end product, "bio-inspired spider silk," has multiple uses.

Bacteria-Eating Plastic To Produce Spider Silk

Researchers at Rensselaer Polytechnic Institute have created a bacterial strain that can convert waste plastic into a multipurpose, biodegradable spider silk. In a new study, they created a high-value protein product using bacteria to change polyethylene plastic, frequently used in single-use products.

The product has uses in textiles, cosmetics, and even medicine. The researchers call it "bio-inspired spider silk" because it resembles the silk spiders use to build their webs.

"Spider silk is nature's Kevlar," said Helen Zha, Ph.D., an assistant professor of chemical and biological engineering and one of the RPI researchers leading the project. "It can be nearly as strong as steel under tension. However, it's six times less dense than steel, so it's very lightweight. As a bioplastic, it's stretchy, tough, nontoxic, and biodegradable."

According to Zha, all those qualities make it an excellent material for a time when using renewable resources and avoiding chronic plastic pollution are standard.

The world's primary source of plastic pollution is polyethylene plastic, which is present in items like food packaging, water bottles, and plastic bags. It can take up to a millennium for polyethylene plastic to organically disintegrate. The bacteria employed in the study may be able to "upcycle" some of the leftover waste because polyethylene plastic is only partially recycled.

The bacteria employed in the study, Pseudomonas aeruginosa, may naturally exploit polyethylene as a food supply. The RPI group took on the task of genetically modifying this bacterium to produce a silk protein with genetic encoding.

They discovered, somewhat surprisingly, that their newly created bacteria could produce the silk protein at a yield comparable to several bacteria more commonly employed in biomanufacturing.

How They Used the Bacteria To Convert Plastic Into Bio-Inspired Spider Silk

People have been using the underlying biological process of this breakthrough for thousands of years.

In essence, the plastic is being fermented by the bacteria. According to Mattheos Koffas, Ph.D., Dorothy and Fred Chau ʼ71 Career Development Constellation Professor in Biocatalysis and Metabolic Engineering, and the other researcher spearheading the project, fermentation is used to make and preserve a wide variety of foods, including cheese, bread, and wine, as well as to produce antibiotics, amino acids, and organic acids in the biochemical industries.

First, according to Zha, the plastic is "predigested" to encourage microorganisms to ferment polyethylene. Similar to how humans must chop and chew their food before their bodies can utilize it, bacteria also find it challenging to consume the lengthy chains of molecules, or polymers, that make up polyethylene.

Zha and Koffas worked on the study with scientists at Argonne National Laboratory, who heated the plastic under pressure to depolymerize it and create a soft, waxy material. Subsequently, the group covered the flask bottoms with a wax coating generated from plastic, which acted as a source of nutrients for the bacterial colony. This contrasts with conventional fermentation, which obtains its nutrients from carbohydrates.

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